Quantum Science 101

The Properties and Applications of Quantum Dots

Image Credit: Shutterstock.com / l i g h t p o e t

Quantum dots (QD) are semiconductor nanocrystals which exhibit quantum mechanical behaviour. The interesting electronic properties of quantum dots arise from the specific size of their energy band gaps.

The Properties of Quantum Dots

These tiny nanoparticles have a diameters which range from 2 nanometres to 10 nanometres, with their electronic characteristics depending on their size and shape. Manufacturers are able to accurately control the size of a quantum dot and as a result they are able ‘tune’ the wavelength of the emitted light to a specific colour.

Quantum dots find applications in a number of areas such as solar cells, transistors, LEDs, medical imaging and quantum computing, thanks to their unique electronic properties.

Optical Applications 

The high extinction coefficient of a quantum dot makes it perfect for optical uses. Quantum dots of very high quality can be ideal for applications in optical encoding and multiplexing due to their narrow emission spectra and wide excitation profiles.

Light Emitting Diodes 

Quantum dot light emitting diodes (QD-LED) and ‘QD-White LED’ are very useful when producing the displays for electronic devices due to the fact that they emit light in highly specific Gaussian distributions. QD-LED displays can render colours very accurately and use much less power than traditional displays.

Image Credit: Shutterstock.com / Kristina Postnikova

Photodetectors 

Quantum dot photodetectors (QDPs) can be produced from traditional single-crystalline semiconductors or solution-processed. Solution-processed QDPs are ideal for the integration of several substrates and for use in integrated circuits. These colloidal QDPs find use in machine vision, surveillance, spectroscopy, and industryial inspection.

Photovoltaics 

Quantum dot solar cells are much more efficient and cost-effective when compared to their silicon solar cells counterparts. Quantum dot solar cells can be produced using simple chemical reactions and can help to save manufacturing costs as a result.

Biological Applications 

The latest generation of quantum dots have great potential for use in biological analysis applications. They are widely used to study intracellular processes, tumour targeting, in vivo observation of cell trafficking, diagnostics and cellular imaging at high resolutions.

Quantum dots have been proved to be far superior to conventional organic dyes as a result of their high quantum yield, photostability and tunable emission spectrum. They are 100 times more stable and 20 times brighter than traditional fluorescent dyes.

The extraordinary photostability exhibited by quantum dots make them ideal for use in ultra-sensitive cellular imaging. This allows several consecutive focal-plane images to be reassembled into three-dimensional images at very high resolution.

Quantum dots can target specific cells or proteins using peptides, antibodies or ligands and then observed in order to study the target protein or the behaviour of the cells. Researchers have found out that quantum dots are far better at delivering the siRNA gene-silencing tool to target cells than currently used methods.

Quantum Computing 

Quantum dots have paved the way for powerful ‘supercomputers’ known as quantum computers. Quantum computers operate and store information using quantum bits or ‘qubits’, which can exist in two states – both on and off simultaneously.

This remarkable phenomenon enables information processing speeds and memory capacity to both be greatly improved when compared to conventional computers.

The Future of Quantum Dots

Quantum dots are zero dimensional and exhibit sharper density of states than structures of higher dimensions. This explains their excellent optical and transport properties, which are currently being studied for potential uses in amplifiers, biological sensors and diode lasers.

The broad range of real-time applications of quantum dots in the field of biology is expected to be very useful in many research disciplines such as cancer metastasis, embryogenesis, lymphocyte immunology and stem cell therapeutics.

In the future researchers also believe that quantum dots can be used as the inorganic fluorophore in intra-operative tumour detection when performed using fluorescence spectroscopy.

References and Further Reading

 

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